This section introduces aspects that may facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Long Term Evolution (LTE) and LTE-Advanced (LTE-A) standards and/or protocols defined by the Third Generation Partnership Project (3GPP, 3GPP2) are one of the next generation cellular communication standards. According to the multiplexing method, LTE and LTE-A systems include two modes, Frequency Division Duplex (FDD) and Time Division Duplex (TDD). Service providers are expected to implement both types of systems depending on the circumstances of the deployment scenario. The advantages to deploying a TDD system include providing flexible resource utilization (e.g., based on traffic characteristics) through different uplink-downlink (UL-DL) configurations.
To meet LTE-A requirements, support of wider transmission bandwidths is required than the 20 MHz bandwidth specified in 3GPP Release 8/9. The preferred solution to this is Carrier Aggregation (CA). In CA, two or more Component Carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A user equipment (UE) may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. Combined with inter-band CA, more flexibility can be achieved using carrier aggregation of FDD band and TDD band.
In LTE Release 10, carrier aggregation of FDD and carrier aggregation of TDD with same UL-DL configuration are supported to get higher data rate and higher spectral efficiency. In LTE Release 11, carrier aggregation of TDD with different UL-DL configurations on different bands is also supported to further improve the data rate and spectral efficiency. In 3GPP TSG RAN meeting #58, RP-122022, “Further LTE Carrier Aggregation Enhancements”, carrier aggregation of FDD and TDD is proposed as a work item. In CA of FDD and TDD, either TDD or FDD can be configured as primary cell (Pcell).
Pcell is the cell operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure, or the cell indicated as the primary cell in the handover procedure. Secondary cell (Scell) is a cell operating on a secondary frequency, which may be configured once an RRC connection is established and which may be used to provide additional radio resources. For a UE in RRC_CONNECTED configured with CA, the term “serving cells” is used to denote the set of one or more cells comprising of the primary cell and all secondary cells.
In order to prepare against a decoding failure that occurs at initial transmission, LTE/LTE-A adopts Hybrid Automatic Repeat Request (HARQ) for retransmission of the decoding-failed data on the physical layer.
HARQ is a technique in which, when decoding fails, the receiver sends the transmitter a Negative ACKnowledgement (NACK) such that the transmitter retransmits the decoding-failed data. If the data is decoded successfully, the receiver sends the transmitter an ACKnowledgement (ACK) such that the transmitter sends new data.
Normally, the HARQ feedback corresponding to physical downlink channel, for example, Physical Downlink Shared CHannel (PDSCH) is transmitted on physical uplink channel, such as Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH), according to predefined timing, and the HARQ feedback corresponding to physical uplink channel, for example, Physical Uplink Shared CHannel (PUSCH) is transmitted on physical downlink channel, such as Physical Hybrid ARQ Indicator CHannel (PHICH), according to predefined timing.
In European patent application EP2530863A2, a method for defining physical channel transmit/receiving timings and resource allocation is provided for use in a TDD system supporting CA.
However, in the prior art, there is no solution for defining HARQ feedback timing for a communication system supporting CA of FDD and TDD.